Peck drilling operations typically require temporary pauses to clear chips and other debris from the drill hole. These periodic pauses are referred to as "peck" cycles. During each peck cycle, feeding of the drill bit into a workpiece is temporarily interrupted at predetermined increments of travel into the workpiece. For example, the feeding operation may be interrupted for 0.1 second every 0.01 inch of travel. Further, the peck cycles may be mixed with full retract cycles, whereby the drill bit is fully retracted from the hole. For example, a retract cycle may be programmed for every 0.1 inch of travel, such that a full retract cycle is programmed for every tenth peck cycle. Full retract cycles are typically used when drilling relatively deep holes in order to avoid chip packing and prevent excessive accumulation of chips in the drill hole.
Sophisticated drilling requires that the drilling apparatus be able to perform a variety of complex peck drilling operations and to automatically detect various conditions, such as dull or broken drill bits, a transition between materials requiring adjustment of the bit feed and rotation rates, and breakthrough when the bit exits the workpiece. According to prior practice, it has not been possible to determine the aforementioned conditions (i.e., dull or broken bits, transition between materials, and breakthrough) during peck drilling because during each peck cycle there is little, if any, thrust or torque on the drill bit. Therefore, because of the rapid decrease in the thrust and torque on the drill bit during each peck cycle, the peck cycle may be mistaken for one of the other conditions (e.g., broken bit or breakthrough).
There is therefore a need in the art of peck drilling to be able to determine when the drill is in a peck cycle in order to distinguish between a peck cycle and other drill bit conditions, such as a broken bit condition or a breakthrough condition.